A new study suggests that a variant of a recently discovered gene may double the risk of lifelong depression after childhood abuse.

CHRONIC DEPRESSION AFTER CHILDHOOD ABUSE MAY BE LINKED TO A NEW GENE

The age-old debate about “nature versus nurture” has become increasingly complicated as we continue to learn more about the impact of individual genes on our risk for various illnesses. While it has become widely accepted that specific genetic patterns may predispose some of us to a very high risk of certain physical illnesses, such as cancer and cardiovascular disease, the potential linkage between specific genes and the risk of mental illness has been less clear. At the same time, however, it has long been known that some mental health disorders, including depression, anxiety disorder, panic disorder, bipolar disorder, and schizophrenia, tend to run in families, which suggests that there may be at least some genetic component to these illnesses.

Over the past 5 years, fundamental new research has begun to suggest that certain genes may indeed be associated with an increased risk of specific mental illnesses. However, most mental health experts believe that having a specific form of a gene linked to mental illness does not, by itself, mean that an affected individual faces a 100 percent risk of developing a mental illness. Getting back to that “nature versus nurture” debate once again, it appears that having a genetic variant associated with a specific mental health illness probably predisposes an affected person to develop that particular mental health disorder, but does not guarantee that this will happen. More specifically, an individual person’s experiences and environment during early life (i.e., the “nurture”) appear to have a significant impact on whether or not genes associated with an increased risk of mental illness (i.e., the “nature”) will actually lead to the development of mental illness.

Now, a newly published clinical study provides strong evidence that a specific form of a single gene can significantly increase the likelihood of major depression in adults following physical abuse during childhood, while another variant of this same gene appears to decrease the risk of chronic depression in similarly abused adults. This intriguing research study appears in the current issue of the Archives of General Psychiatry.

This new research study was inspired by previous research with laboratory animals that identified a network of neurons in the brain that use chemicals called endocannabinoids to communicate with each other. (If the word “endocannabinoid” sounds vaguely familiar, it is because these naturally occurring neurotransmitters in the brain also have counterparts in the plant world, most notably in cannabis, or marijuana, plants!) Previous research has also suggested that the endocannabinoid system in the brain may play an important role in adaptation to stress, including the moderation of our mood following stressful events.

In this new study, two groups of patient-volunteers were included. The first group consisted of 1,041 young adult female twins in the United States, while the second group consisted of 1,428 Australian adults known to be addicted to heroin. (An additional 506 Australian volunteers without heroin addiction participated in this study as the control group for the heroin-addicted volunteers.) The presence of depression, and in particular, depression with anhedonia (a term that indicates the inability to enjoy experiences that most of us find pleasurable), was assessed among all of these patient-volunteers. The absence or presence of a history of physical abuse, by a parent or caregiver, during childhood was also evaluated. Testing of the gene which codes for the human endocannabinoid receptor in the brain was performed on all of these research volunteers, as well.

The findings of this study were highly significant. Not surprisingly, the study volunteers who reported having experienced significant childhood physical abuse had a much higher incidence of depression when compared to those volunteers who did not experience physical abuse as children. Among the volunteers who had experienced significant physical abuse during childhood, a single, specific variant of the endocannabinoid receptor gene appeared to be highly protective against anhedonic depression when compared to volunteers who possessed the more common variant of this gene. Specifically, only 29 percent of abused volunteers with this less common variant of the endocannabinoid receptor gene experienced anhedonic symptoms, while 57 percent of the previously abused volunteers with the most common form of this same gene were found to have symptoms of anhedonic depression.

The findings of this study strongly suggest that certain naturally occurring variants of specific genes may either increase or decrease the risk of mental illness (and in the case of this clinical study, major depression with anhedonia) following stressful experiences earlier in life. Not only do this study’s findings suggest a method of screening patients who might be at significantly increased risk for major depression following stressful events in their early lives, but the linkage of a specific gene within the brain’s endocannabinoid system with depression following traumatic childhood experiences may someday allow for a more effective treatment for post-traumatic major depression, using medications targeted at the specific genetic variation that leads to this increased risk of depression following childhood trauma.

At this time, more than 8 percent of Americans are unemployed. According to the Bureau of Labor Statistics, however, the unemployment rate for veterans who served on active duty between September 2001 and December 2011 is now more than 12 percent. A new website, Veterans in Healthcare, seeks to connect veterans with potential employers. If you are a veteran who works in the healthcare field, or if you are an employer who is looking for physicians, advanced practice professionals, nurses, corpsmen/medics, or other healthcare professionals, then please take a look at Veterans in Healthcare. As a retired veteran of the U.S. Army, I would also like to personally urge you to hire a veteran whenever possible.

Disclaimer: As always, my advice to readers is to seek the advice of your physicianbeforemaking any significant changes in medications, diet, or level of physical activity

Dr. Wascher is an oncologic surgeon, professor of surgery, cancer researcher, oncology consultant, and a widely published author

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